Planning and facilitation systems and methods for cryosurgery

ABSTRACT

Systems and methods for planning a cryoablation procedure and for facilitating a cryoablation procedure utilize integrated images displaying, in a common virtual space, a three-dimensional model of a surgical intervention site based on digitized preparatory images of the site from first imaging modalities, simulation images of cryoprobes used according to an operator-planned cryoablation procedure at the site, and real-time images provided by second imaging modalities during cryoablation. The system supplies recommendations for and evaluations of the planned cryoablation procedure, feedback to an operator during cryoablation, and guidance and control signals for operating a cryosurgery tool during cryoablation. Methods are provided for generating a nearly-uniform cold field among a plurality of cryoprobes, for cryoablating a volume with smooth and well-defined borders, thereby minimizing damage to healthy tissues.

RELATED APPLICATIONS

The present application is a Continuation of U.S. patent applicationSer. No. 11/066,294, filed on Feb. 28, 2005, which is a Divisional ofU.S. patent application Ser. No. 09/917,811, filed on Jul. 31, 2001, nowU.S. Pat. No. 6,905,492, issued on Jun. 14, 2005, which claims priorityfrom U.S. Provisional Patent Application No. 60/221,891, filed on Jul.31, 2000. The contents of all of the above-mentioned applications areherein incorporated by reference.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to cryosurgical systems and methodsuseable for planning and for facilitating a cryoablation procedure. Moreparticularly, the present invention relates to the use of integratedimages displaying, in a common virtual space, images of athree-dimensional model of a surgical intervention site, simulationimages of a planned cryoablation procedure at the site, and real-timeimages of the site during cryoablation. The present invention furtherrelates to system-supplied recommendations for, and evaluations of, aplanned cryoablation procedure, and to system-supplied feedback to anoperator and system-supplied control signals to a cryosurgery toolduring cryoablation.

Cryosurgical procedures involve deep tissue freezing which results intissue destruction due to rupture of cells and or cell organelles withinthe tissue. Deep tissue freezing is effected by insertion of a tip of acryosurgical device into the tissue, either transperineally,endoscopically or laparoscopically, and a formation of, what is known inthe art as, an ice-ball around the tip.

In order to effectively destroy a tissue by such an ice-ball, thediameter of the ball should be substantially larger than the region ofthe tissue to be treated, which constraint derives from the specificprofile of temperature distribution across the ice-ball.

Specifically, the temperature required for effectively destroying atissue is about −40° C., or cooler. However, the temperature at thesurface of the ice-ball is 0° C. The temperature declines exponentiallytowards the center of the ball such that an isothermal surface of about−40° C. is typically located within the ice-ball substantially at thehalf way between the center of the ball and its surface.

Thus, in order to effectively destroy a tissue there is a need to locatethe isothermal surface of −40° C. at the periphery of the treatedtissue, thereby exposing adjacent, usually healthy, tissues to theexternal portions of the ice-ball. The application of temperatures ofbetween about −40° C. and 0° C. to such healthy tissues usually causessubstantial damage thereto, which damage may result in temporary orpermanent impairment of functional organs.

In addition, when the adjacent tissues are present at opposite borderswith respect to the freeze treated tissue, such as in the case ofprostate freeze treatments, as is further detailed below, and since thegrowth of the ice-ball is in substantially similar rate in alldirections toward its periphery, if the tip of the cryosurgical deviceis not precisely centered, the ice-ball reaches one of the bordersbefore it reaches the other border, and decision making of whether tocontinue the process of freezing, risking a damage to close healthytissues, or to halt the process of freezing, risking a non-completedestruction of the treated tissue, must be made.

Although the present invention is applicable to any cryosurgicaltreatment, discussion is hereinafter primarily focused on a cryosurgicaltreatment of a patient's prostate.

Thus, when treating a tumor located at a patient's prostate, there is atrade-of between two options: (a) effectively destroying the prostatictissue extending between the prostatic urethra and the periphery of theprostate and causing unavoidable damage to the patient's urethra ororgans adjacent the prostate such as the rectum and nerves; (b) avoidingthe damaging of the prostatic urethra and adjacent organs, but exposingthe patient to the risk of malignancy due to ineffective destruction ofthe prostate tumor. Treatment of benign prostate hyperplasia (BPH),while not requiring total destruction of an entire volume of prostatetissue as does treatment of a malignancy, nevertheless does run the riskof causing damage to healthy functional tissues and organs adjacent tothe prostate, if care is not taken to limit the scope of destructivefreezing to appropriate locations.

A classical cryosurgery procedure for treating the prostate includes theintroduction of 5-7 probes into the prostate, the probes being typicallyarranged around the prostatic urethra such that a single probe islocated, preferably centered, between the prostatic urethra and theperiphery of the prostate. The dimensions of such a single-probe areusually adapted for effectively treating the prostatic tissue segmentextending from the urethra to the periphery of the prostate, e.g., a tipof 3 millimeters in diameter, generating an ice-ball of 3-4 centimetersin diameter, depending on the size of the prostate. Since a singleice-ball is used for freezing such a prostatic tissue segment, thevolume of adjacent tissues exposed to damage is substantially greaterthan the volume of the treated tissue. For example, if the area of theice-ball in cross section is πR², and an effective treatment of at least−40° C. is provided to an area of π(R/2)² (in cross section), then thearea of adjacent tissues (in cross section) exposed to between about−40° C. and about 0° C. is πR^(2−0.25)(πR²)=0.75(πR²), which is threetimes the area of the tissue effectively treated by the ice-ball.

A modification of the classic cryosurgery procedure described in thepreceding paragraph, intended to avoid excessive damage to adjacenttissues, is to use such a single probe of a smaller diameter producingan ice-ball of smaller size. Such a modification, however, exposes thepatient to the danger of malignancy because of a possible incompletedestruction of the tumor.

The classical cryosurgery procedure herein described, therefore, doesnot provide effective resolution of treatment along the planesperpendicular to the axis of penetration of the cryosurgical probe intothe patient's organ.

A further limitation of the classical procedure stems from the fact thatanatomical organs such as the prostate usually feature an asymmetricthree-dimensional shape. Consequently, introduction of a cryosurgicalprobe along a specific path of penetration within the organ may provideeffective treatment to specific regions located at specific depths ofpenetration but at the same time may severely damage other portions ofthe organ located at other depths of penetration.

U.S. Pat. No. 6,142,991 to Schatzberger teaches a high resolutioncryosurgical method and device for treating a patient's prostatedesigned to overcome the described limitations of the classicalcryosurgery procedure described hereinabove. Schatzberger's “highresolution” method (referred to as the “HR method” hereinbelow)comprises the steps of (a) introducing a plurality of cryosurgicalprobes to the prostate, the probes having a substantially small diameterand are distributed across the prostate, so as to form an outerarrangement of probes adjacent the periphery of the prostate and aninner arrangement of probes adjacent the prostatic urethra; and (b)producing an ice-ball at the end of each of said cryosurgical probes, soas to locally freeze a tissue segment of the prostate. Schatzberger'sapparatus (referred to hereinbelow as the “HR” apparatus) comprises (a)a plurality of cryosurgical probes of small diameter, the probes servefor insertion into the patient's organ, the probes being for producingice-balls for locally freezing selected portions of the organ; (b) aguiding element including a net of apertures for inserting thecryosurgical probes therethrough; and (c) an imaging device forproviding a set of images, the images being for providing information onspecific planes located at specific depths within the organ, each ofsaid images including a net of marks being correlated to the net ofapertures of the guiding element, wherein the marks represent thelocations of ice-balls which may be formed by the cryosurgical probeswhen introduced through said apertures of the guiding element to saiddistinct depths within the organ.

The HR method and device provide the advantages of high resolution oftreatment along the axis of penetration of the cryosurgical probe intothe patient's organ as well as along the planes perpendicular to theaxis of penetration, thereby enabling to effectively destroy selectiveportions of a patient's tissue while minimizing damage to adjacenttissues and organs, and to selectively treat various portions of thetissue located at different depths of the organ, thereby effectivelyfreezing selected portions of the tissue while avoiding the damaging ofother tissues and organs located at other depth along the axis ofpenetration.

Schatzberger, in U.S. Pat. No. 6,142,991 also teaches the additionalstep of three dimensionally mapping an organ of a patient so as to forma three dimensional grid thereof, and applying a multi-probe systemintroduced into the organ according to the grid, so as to enablesystematic high-resolution three dimensional cryosurgical treatment ofthe organ and selective destruction of the treated tissue with minimaldamage to surrounding, healthy, tissues.

It is, however, a disadvantage of the HR apparatus and method as taughtin U.S. Pat. No. 6,142,991 that the apparatus enables, and the methodrequires, a high level of diagnostic sophistication in the selection anddefinition of the particular volume of tissue to be cryoablated.Real-time imaging capabilities of the HR apparatus provide for imagingof the target organ at a selected depth of penetration and therebyassist an operator in deciding where to introduce and utilize aplurality of cryogenic probes, yet the complex three-dimensionalgeometry of the cryoablation target is poorly rendered by the set of twodimensional images constituting the three dimensional grid ascontemplated by the HR method and apparatus. In this prior art method,little assistance is provided for an operator in understanding the threedimensional shape and structure of the cryoablation target and thesurrounding tissues. Information vital to the operator may be present inthe set of images, yet difficult for the operator to see and appreciate.In a set of images of this type, the details may be present, yet it maybe difficult to appreciate their significance because of the difficultyof seeing them in context. A three dimensional “grid” composed of aplurality of two dimensional images such as ultrasound images containmany details, yet do not facilitate the understanding of those detailsin a three dimensional context.

Thus there is a widely recognized need for, and it would be highlyadvantageous to have, an apparatus for facilitating cryosurgery whichprovides real-time imaging of a cryoablation target site in a mannerwhich is easy for an operator to visualize and to understand.

It is an additional limitation of the HR method and apparatus, and ofother prior art systems, that the imaging capabilities contemplated arenot well adapted to assist an operator in planning a cryoablationprocedure. In addition to the fact that the imaging facilities thereprovided are poorly adapted to visualization of the three dimensionalspace by an operator, they are also limited in that the apparatus ispoorly adapted to providing images of the target area in advance of theoperation, e.g., for planning purposes. The described HR equipmentmight, of course, but used to create the described three dimensionalmapping of the target area well in advance of a surgical intervention,but no mechanism is provided for facilitating the relating the images soobtained, and any planned procedures based on those images, to asubsequent intervention procedure. Moreover, the fact that the imagingmodality of the HR apparatus is physically connected to parts of thecryosurgery equipment limits its versatility and may in some cases makeit awkward to use for creating preparatory images of an interventionsite.

Thus there is a widely recognized need for, and it would be highlyadvantageous to have, an apparatus for planning and for facilitatingcryosurgery which provides easily understandable visualization of acryoablation target site in advance of a surgical intervention, whichfurther provides facilities for studying the site and for planning theintervention, and which yet further provides facilities for applyinginformation gleaned from prior study of the imaged site, and specificplans for intervening in the site, to the actual site, in real time,during the planned cryoablation operation.

It is a further limitation of the HR method that no means are providedfor facilitating the relating of images obtained in advance of asurgical intervention to a subsequent intervention. Yet whereasultrasound images of a target site can be generated in real time duringan intervention, and MRI techniques may also (if somewhat less easily)also be obtained during cryosurgery, other imaging techniques (CT scans,for example) are less well adapted to being produced during the courseof an actual cryosurgery intervention.

Thus there is a widely recognized need for, and it would be highlyadvantageous to have, an apparatus and method for facilitating therelating of images obtained prior surgery to real-time images, from thesame or from additional sources, obtained during cryosurgery.

Much is now known about the tissue-destructive processes ofcryoablation, and about the subsequent short-term and long-termconsequences to an organ such as a prostate which has undergone partialcryoablation. The laws of physics relating to the conduction of heat ina body, reinforced by experimentation and further reinforced byaccumulated clinical experience in cryosurgery, provide a wealth ofinformation enabling to predict with some accuracy the effect of aspecific planned cryoablation procedure on target tissues. Thisinformation, and this capability for prediction, is underutilized incurrent cryosurgery practice.

The Seednet Training And Planning Software (“STPS”) marketed by GalilMedical Ltd. of Yokneam, Israel constitutes a set in this direction, inthat it provides a system for displaying, and allowing an operator tomanipulate, a three-dimensional model of a prostate, and further allowsan operator to plan a cryoablation intervention and to visualize thepredicted effect of that planned intervention on the prostate tissues.STPS, however, is limited in that it does not provide means for relatinga preliminary three dimensional model of a prostate to the prostate asrevealed in real-time during the course of a surgical procedure.Moreover, the predictive ability of the STPS system is limited topredicting the extent of the freezing produced by a given deployment ofa plurality of cryoprobes over a given time. No assistance is providedto an operator in discerning interactions between the predictedcryoablation and specific structures desired to be protected or to bedestroyed. No assistance is given in predicting long-term effects of agiven cryoablation procedure. No assistance is given in recommendingprocedures, placement of probes, temperature, or timing of anintervention.

Thus there is a widely recognized need for, and it would be highlyadvantageous to have, apparatus and method for calculating probableimmediate, short-term, and long-term effects of a planned cryoablationprocedure, thereby to facilitate the planning of such a procedure. Thereis further a widely recognized need for, and it would be highlyadvantageous to have, apparatus and method for facilitating theimplementation of such a planned procedure, in real time, duringexecution of a planned cryoablation.

It is noted that with respect to BPH, the need for such a planning andfacilitation apparatus is particularly strong.

BPH, which affects a large number of adult men, is a non-cancerousenlargement of the prostate. BPH frequently results in a gradualsqueezing of the portion of the urethra which traverses the prostate,also known as the prostatic urethra. This causes patients to experiencea frequent urge to urinate because of incomplete emptying of the bladderand a burning sensation or similar discomfort during urination. Theobstruction of urinary flow can also lead to a general lack of controlover urination, including difficulty initiating urination when desired,as well as difficulty in preventing urinary flow because of the residualvolume of urine in the bladder, a condition known as urinaryincontinence. Left untreated, the obstruction caused by BPH can lead toacute urinary retention (complete inability to urinate), serious urinarytract infections and permanent bladder and kidney damage.

Most males will eventually suffer from BPH. The incidence of BPH for menin their fifties is approximately 50% and rises to approximately 80% bythe age of 80. The general aging of the United States population, aswell as increasing life expectancies, is anticipated to contribute tothe continued growth in the number of BPH sufferers.

Patients diagnosed with BPH generally have several options fortreatment: watchful waiting, drug therapy, surgical intervention,including transurethral resection of the prostate (TURP), laser assistedprostatectomy and new less invasive thermal therapies.

Various disadvantages of existing therapies have limited the number ofpatients suffering from BPH who are actually treated. In 1999, thenumber of patients actually treated by surgical approaches was estimatedto be 2% to 3%. Treatment is generally reserved for patients withintolerable symptoms or those with significant potential symptoms iftreatment is withheld. A large number of the BPH patients delaydiscussing their symptoms or elect “watchful waiting” to see if thecondition remains tolerable.

Thus, development of a less invasive, more convenient, or moresuccessful treatment for BPH could result in a substantial increase inthe number of BPH patients who elect to receive interventional therapy.

Cryoablation is a candidate for being such a popularize treatment.

With respect to drug therapies: some drugs are designed to shrink theprostate by inhibiting or slowing the growth of prostate cells. Otherdrugs are designed to relax the muscles in the prostate and bladder neckto relieve urethral obstruction. Current drug therapy generally requiresdaily administration for the duration of the patient's life.

With respect to surgical interventions: the most common surgicalprocedure, transurethral resection of the prostate (TURP), involves theremoval of the prostate's core in order to reduce pressure on theurethra. TURP is performed by introducing an electrosurgical cuttingloop through a cystoscope into the urethra and “chipping out” both theprostatic urethra and surrounding prostate tissue up to the surgicalcapsule, thereby completely clearing the obstruction. It will beappreciated that this procedure results in a substantial damageinflicted upon the prostatic urethra.

With respect to laser ablation of the prostate: laser assistedprostatectomy includes two similar procedures, visual laser ablation ofthe prostate (V-LAP) and contact laser ablation of the prostate (C-LAP),in which a laser fiber catheter is guided through a cystoscope and usedto ablate and coagulate the prostatic urethra and prostatic tissue.Typically, the procedure is performed in the hospital under eithergeneral or spinal anesthesia, and an overnight hospital stay isrequired. In V-LAP, the burnt prostatic tissue then necroses, or diesand over four to twelve weeks is sloughed off during urination. InC-LAP, the prostatic and urethral tissue is burned on contact andvaporized. Again, it will be appreciated that these procedures result ina substantial damage inflicted upon the prostatic urethra.

With respect to heat ablation therapies: these therapies, underdevelopment or practice, are non-surgical, catheter based therapies thatuse thermal energy to preferentially heat diseased areas of the prostateto a temperature sufficient to cause cell death. Thermal energy formsbeing utilized include microwave, radio frequency (RF) and highfrequency ultrasound energy (HIFU). Both microwave and RF therapysystems are currently being marketed worldwide. Heat ablationtechniques, however, burn the tissue, causing irreversible damage toperipheral tissue due to protein denaturation, and destruction of nervesand blood vessels. Furthermore, heat generation causes secretion ofsubstances from the tissue which may endanger the surrounding area.

With respect to transurethral RF therapy: transurethral needle ablation(TUNA) heats and destroys enlarged prostate tissue by sending radiowaves through needles urethrally positioned in the prostate gland. Theprocedures prolongs about 35 to 45 minutes and may be performed as anoutpatient procedure. However TUNA is less effective than traditionalsurgery in reducing symptoms and improving urine flow. TUNA also burnthe tissue, causing irreversible damage to peripheral tissue due toprotein denaturation, and destruction of nerves and blood vessels.Furthermore, as already discussed above, heat generation causessecretion of substances from the tissue which may endanger thesurrounding area.

In contrast to the alternative treatments for BPH listed above,cryoablation therapy presents significant advantages. The volume of anenlarged prostate can be reduced, and stricture to the urethra can beeliminated, by selective destruction of prostate tissue by cryoablation.Tissues destroyed by cryoablation in treating BPH are gradually absorbedby the body, rather than being sloughed off during urination.

When the tissues to be cryoablated are appropriately selected andaccurately cryoablated, there may be minimal endangerment of vitalhealthy functional tissues in proximity to the prostate. Thus,cryoablation is an important technique for treating BPH and haspotential for becoming an increasingly popular therapy and enablingtreatment of a large population of sufferers who today receive noeffective treatment at all for their condition.

Thus, there is a widely recognized need for, and it would be highlyadvantageous to have, apparatus and method facilitating the planningcryoablation for the treatment of BPH by recommending appropriate numberor placement of loci for cryoablation based on a patient'ssymptomatology, thereby helping to make this useful therapy accessibleto surgeons not specialized in this specific method of treatment.

Particularly for surgeons who are not specialists in the particularlimited field of cryoablation of the prostate, there is a widelyrecognized need for, and it would be highly advantageous to have,apparatus and method which facilitates the execution of a plannedcryoablation treatment of the prostate or of another organ by providingfeedback on the progress of an intervention by comparing real-timeimaging of the intervention site with a planning model of the site,providing warnings when freezing, visible in ultrasound, approachesareas designated as needing to be protected from damage, or whendestruction of tissues risks failing to cover volumes designated asrequiring to be destroyed. Similarly, there is a widely recognized needfor, and it would be highly advantageous to have, mechanisms for guidingmovements of an operator during a cryoablation procedure, or forautomatically managing the movement of cryosurgical tools such ascryoprobes during a cryoablation intervention, according to informationbased on a plan of the intervention and feedback obtained throughreal-time imaging of the intervention site.

In one respect, a system for planning a cryoablation intervention isparticularly useful. Prior art has given little consideration to theinteractive effects of a plurality of closely placed cryoprobes. Yettissues which are in proximity to two or more cryoprobes may be cooledby several sources simultaneously, and consequently achieve a lowertemperature than would be expected when considering the well-knownfreezing patterns created by a single cryoprobe used in isolation.

Thus there is a widely recognized need for, and it would be highlyadvantageous to have, system and method for utilizing a plurality ofcryoprobes that takes into account their mutually-reinforcing coolingeffect to create a near-uniform cold field within a volume. It wouldfurther be advantageous to have a system and method for defining avolume in which cognizance is take of the mutually reinforcing coolingeffect of a plurality of closely placed cryoprobes to smoothly andaccurately define a border of a cryoablation volume, thereby ensuringtotal destruction of tissues within that volume while minimizing damageto tissues outside that volume.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided aplanning system for planning a cryosurgical ablation procedure,comprising a first imaging modality for creating digitized preparatoryimages of an intervention site, a three-dimensional modeler for creatinga three-dimensional model of the intervention site based on thedigitized preparatory images; and a simulator for simulating acryosurgical intervention, having an interface useable by an operatorfor specifying loci for insertion of cryoprobes and operationalparameters for operation of the cryoprobes for cryoablating tissues, anda displayer for displaying in a common virtual space an integrated imagecomprising a display of said three-dimensional model of saidintervention site and a virtual display of cryoprobes inserted at saidloci.

According to further features in preferred embodiments of the inventiondescribed below, the planning system further comprises a memory forstoring said specified loci for insertion of cryoprobes and saidoperational parameters for operation of said cryoprobes.

According to still further features in the described preferredembodiments the first imaging modality is selected from the groupconsisting of magnetic resonance imaging, ultrasound imaging andcomputerized tomography imaging, and the three-dimensional model isexpressible in a three-dimensional Cartesian coordinate system.

According to still further features in the described preferredembodiments the interface also serves for highlighting selected regionswithin the three-dimensional model, and the integrated image furthercomprises a display of an operator-highlighted regions. The interface isuseable by an operator for identifying tissues to be cryoablated and foridentifying tissues to be protected from damage during cryoablation, andthe integrated image further comprises a display of saidoperator-identified tissues to be cryoablated and of saidoperator-identified tissues to be protected from damage during saidcryoablation.

According to still further features in the described preferredembodiments the system further comprises a predictor for predicting aneffect on tissues of the patient of operation of the cryoprobes at theloci according to the operational parameters, and the model displayeradditionally displays in the common virtual space a representation ofthe predicted effect.

According to still further features in the described preferredembodiments, the system further comprises an evaluator for comparing thepredicted effect to an operator-defined goal of the procedure. Theevaluator is for identifying areas of predicted less-than-totaldestruction of tissues within a volume of desired total destruction oftissues as defined by an operator, and for identifying areas specifiedas requiring protection during cryoablation which may be endangered by aspecified planned cryoablation procedure.

According to still further features in the described preferredembodiments, the system comprises a recommender for recommendingcryosurgical procedures to an operator, the recommendation being basedon goals of a cryoablation procedure, the goals being specified by anoperator, and further being based on the three-dimensional model of thesite, thereby facilitating planning the cryoablation procedure. Therecommender may recommend an optimal number of cryoprobes for use in acryoablation procedure, or an optimal temperature for a cryoprobe foruse in a cryoablation procedure, or an optimal duration of cooling for acryoprobe for use in a cryoablation procedure. The recommendation may bebased on a table of optimal interventions based on expertrecommendations, or on a table of optimal interventions based oncompiled feedback from a plurality of operators, and may comprisespecific locations for insertion of a cryoprobe to affect cryoablation.The recommended procedures may be for cryoablation of tissues of aprostate, for treating BPH percutaneously or transperineally, or fortreating a mass or a malignancy. The table may comprise a measure ofvolume of a prostate, or a measure of length of a stricture of a urethraor a measure of symptomatic severity of a BPH condition such as an AUAquestionnaire score.

The recommendation may be of multiple cryoprobes closely placed so as toensure a continuous cold field sufficient to ensure complete destructionof tissues within a target volume, while minimizing damage to tissuesoutside said target volume.

According to another aspect of the present invention there is provided asurgical facilitation system for facilitating a cryosurgery ablationprocedure, comprising a first imaging modality, for creating digitizedpreparatory images of an intervention site, a three-dimensional modelerfor creating a first three-dimensional model of the intervention sitebased on the digitized preparatory images, a second imaging modality,for creating a digitized real-time image of at least a portion of theintervention site during a cryosurgery procedure, and an imagesintegrator for integrating information from the three-dimensional modelof the site and from the real-time image of the site in a commoncoordinate system, thereby producing an integrated image.

According to further features in preferred embodiments of the inventiondescribed below, the surgical facilitation system further comprising aplanning system as described hereinabove.

According to still further features in the described preferredembodiments the surgical facilitation system further comprises adisplayer for displaying the integrated image in a common virtual space.The displayed integrated image may be a two-dimensional image or athree-dimensional image.

According to still further features in the described preferredembodiments the surgical facilitation system further comprises athree-dimensional modeler for creating a second three-dimensional modelof at least a portion of the intervention site based on a plurality ofreal-time images. The images integrator may be operable for integratinginformation from the first three-dimensional model of the site and fromthe second three-dimensional model of at least a portion of the site ina common coordinate system.

According to still further features in the described preferredembodiments the first imaging modality comprises at least one of a groupcomprising magnetic resonance imaging, ultrasound imaging, andcomputerized tomography imaging, and the second imaging modalitycomprises at least one of a group comprising magnetic resonance imaging,ultrasound imaging, and computerized tomography imaging.

According to still further features in the described preferredembodiments the second imaging modality comprises an imaging tooloperable to report a position of the tool during creation of thereal-time image, thereby providing localizing information about thereal-time image useable by the images integrator.

According to still further features in the described preferredembodiments the imaging tool is an ultrasound probe inserted in therectum of a patient and operable to report a distance of penetration inthe rectum of the patient during creation of ultrasound images of aprostate of the patient.

According to still further features in the described preferredembodiments the first three-dimensional model is expressed in athree-dimensional Cartesian coordinate system.

According to still further features in the described preferredembodiments the surgical facilitation system further comprises aninterface useable by an operator for highlighting selected regionswithin the first three-dimensional model and the integrated imagefurther comprises a display of an operator-highlighted region. Theinterface is useable by an operator for identifying tissues to becryoablated or for identifying tissues to be protected from damageduring cryoablation, and integrated image further comprises a display ofoperator-identified tissues to be cryoablated or of operator-identifiedtissues to be protected from damage during said cryoablation. Theinterface is also useable by an operator for labeling topographicfeatures of the first three-dimensional model and of the real-timeimages or of the second three-dimensional model.

According to still further features in the described preferredembodiments the images integrator matches operator-labeled topographicfeatures of the first three-dimensional model with operator-labeledfeatures of the real-time images, to orient the first three-dimensionalmodel and the real-time image with respect to the common coordinatesystem.

According to still further features in the described preferredembodiments the images integrator matches operator-labeled topographicfeatures of the first three-dimensional model with operator-labeledfeatures of the second three-dimensional model, to orient the firstthree-dimensional model and second three-dimensional model with respectto a common coordinate system.

According to still further features in the described preferredembodiments comprises a simulator for simulating a cryosurgicalintervention, the simulator comprising an interface useable by anoperator during a planning phase of the intervention, for specifyingloci for insertion of cryoprobes and operational parameters foroperation of the cryoprobes for cryoablating tissues, the imageintegrator being operable to integrate the operator-specified loci forinsertion of cryoprobes into the integrated image, and the displayerbeing operable to display the integrated image.

According to still further features in the described preferredembodiments the surgical facilitation system further comprises a firstcomparator for comparing the first three-dimensional model with thereal-time image to determine differences, a representation of thedifferences being further displayed by the displayer in the integratedimage.

According to still further features in the described preferredembodiments the surgical facilitation system further comprises apparatusfor providing feedback to an operator regarding position of tools beingused during a surgical intervention as compared to the loci forinsertion of cryoprobes specified by an operator during the planningphase of the intervention. The system further comprises apparatus forproviding feedback to an operator regarding position of tools being usedduring a surgical intervention as compared to operator-identifiedtissues to be cryoablated, and apparatus for providing feedback to anoperator regarding position of tools being used during a surgicalintervention as compared to operator-identified tissues to be protectedduring cryoablation, and apparatus for guiding an operator in theplacement of cryoprobes for affecting cryoablation, the guiding beingaccording to the loci for insertion of cryoprobes specified by anoperating during the planning phase of the intervention.

According to still further features in the described preferredembodiments the surgical facilitation system further comprises apparatusfor limiting movement of a cryoprobes during a cryoablationintervention, the limitation being according to the loci for insertionof cryoprobes specified by an operating during the planning phase of theintervention.

According to still further features in the described preferredembodiments the surgical facilitation system further comprises acryoprobe displacement apparatus for moving at least one cryoprobe to atleast one of the loci for insertion of cryoprobes specified by anoperating during the planning phase of the intervention.

According to still further features in the described preferredembodiments the cryoprobe displacement apparatus comprises a steppermotor and a position sensor, and the surgical facilitation system isoperable to affect cooling of the at least one cryoprobe, heating of atleast one cryoprobe, and is operable to affect scheduled movement of atleast one cryoprobe coordinated with scheduled alternative heating andcooling of at least one cryoprobe, to affect cryoablation at a pluralityof loci.

According to yet another aspect of the present invention there isprovided a cryoablation method for ensuring complete destruction oftissues within a selected target volume while minimizing destruction oftissues outside the selected target volume, comprising deploying aplurality of cryoprobes in a dense array within the target volume, andcooling the cryoprobes to affect cryoablation, while limiting thecooling to a temperature only slightly below a temperature ensuringcomplete destruction of tissues, thereby limiting destructive range ofeach cooled cryoprobe, the plurality of cryoprobes being deployed in anarray sufficiently dense to ensure destruction of tissues within thetarget volume.

According to still further features in the described preferredembodiments the method further comprises a planner for planning thedense array, the planner utilizing a three-dimensional model of thetarget volume to calculate a required density of the dense array ofdeployed cryoprobes operated at a selected temperature, to affectcomplete destruction of tissues within the selected target volume.

According to still further features in the described preferredembodiments the method further comprises using a planner for planningthe dense array, the planner utilizing a three-dimensional model of thetarget volume to calculate, for a plurality of cryoprobes deployed to aselected array of freezing loci, a temperature and duration of coolingfor each of the cryoprobes sufficient to affect complete destruction oftissues within the selected target volume, while also minimizing coolingof tissues outside of the selected target volume.

According to yet another aspect of the present invention there isprovided a cryoablation method ensuring complete destruction of tissueswithin a selected target volume while minimizing destruction of tissuesoutside the selected target volume, comprising utilizing cryoprobes toaffect cryoablation at a plurality of freezing loci, the loci being of afirst type and of a second type, the first type being located adjacentto a surface of the selected target volume and the second type beinglocated at an interior portion of the selected target volume, andcooling cryoprobes deployed at loci of the first type to a first degreeof cooling and cooling cryoprobes deployed at loci of the second type toa second degree of cooling, the first degree of cooling being lesscooling than the second degree of cooling, thereby affecting wide areasof destruction around each cryoprobe deployed at loci of the second typeand narrow areas of destruction around each cryoprobe deployed at lociof the first type, thereby ensuring complete destruction of tissueswithin a selected target volume while minimizing destruction of tissuesoutside the selected target volume.

According to still further features in the described preferredembodiments cryoprobes deployed to freezing loci of the first type arecooled to a first temperature and cryoprobes deployed to freezing lociof the second type are cooled to a second temperature, the secondtemperature being lower than the first temperature.

According to still further features in the described preferredembodiments cryoprobes deployed to freezing loci of the first type arecooled for a first length of time, and cryoprobes deployed to freezingloci of the second type are cooled for a second length of time, thesecond length of time being longer than the first length of time.

According to still further features in the described preferredembodiments the method further comprises a planner for planning thedense array, the planner utilizing a three-dimensional model of thetarget volume to calculate, for a given array of freezing loci, arequired temperature and length of cooling time for loci of the firsttype and for loci of the second type, to affect complete destruction oftissues within the selected target volume while minimizing destructionof issues outside the selected target volume.

According to yet another aspect of the present invention there isprovided a method for planning a cryosurgical ablation procedure,comprising utilizing a first imaging modality to create digitizedpreparatory images of an intervention site, utilizing athree-dimensional modeler to create a three-dimensional model of theintervention site based on the digitized preparatory images, andutilizing a simulator having an interface useable by an operator forspecifying loci for insertion of cryoprobes and for specifyingoperational parameters for operation of the cryoprobes, to specify locifor insertion of cryoprobes and operational parameters for operation ofthe cryoprobes for cryoablating tissues, thereby simulating a plannedcryosurgical ablation procedure.

According to still further features in the described preferredembodiments, the method further comprises utilizing a displayer todisplay in a common virtual space an integrated image comprising adisplay of the three-dimensional model of the intervention site and avirtual display of cryoprobes inserted at the loci, and utilizing amemory to store the specified loci for insertion of cryoprobes and theoperational parameters for operation of the cryoprobes. The firstimaging modality is selected from the group consisting of magneticresonance imaging, ultrasound imaging and computerized tomographyimaging. The three-dimensional model is expressible in athree-dimensional Cartesian coordinate system. The method furthercomprises utilizing the interface to highlight selected regions withinthe three-dimensional model. Highlighting maybe be used to identifytissues to be cryoablated and to identify tissues to be protected fromdamage during cryoablation.

According to still further features in the described preferredembodiments the method further comprises utilizing a predictor topredict an effect on tissues of the patient of operation of thecryoprobes at the loci according to the operational parameters, and themodel displayer additionally displays in the common virtual space arepresentation of the predicted effect.

According to still further features in the described preferredembodiments the method further comprises utilizing an evaluator tocompare the predicted effect to an operator-defined goal of theprocedure.

According to still further features in the described preferredembodiments the method further comprising utilizing the evaluator toidentify areas of predicted less-than-total destruction of tissueswithin a volume of desired total destruction of tissues as defined by anoperator, and utilizing the evaluator to identify areas specified asrequiring protection during cryoablation which may be endangered by aspecified planned cryoablation procedure.

According to still further features in the described preferredembodiments the method further comprises utilizing a recommender forrecommending cryosurgical procedures, the recommendation being based ongoals of a cryoablation procedure, the goals being specified by anoperator, and further being based on the three-dimensional model of thesite. The recommender recommends an optimal number of cryoprobes for usein a cryoablation procedure, an optimal temperature for a cryoprobe foruse in a cryoablation procedure, an optimal duration of cooling for acryoprobe for use in a cryoablation procedure. The recommendation isbased on a table of optimal interventions based on expertrecommendations, or on a table of optimal interventions based oncompiled feedback from a plurality of operators.

According to still further features in the described preferredembodiments the recommendation comprises specific locations forinsertion of a cryoprobe to affect cryoablation.

According to still further features in the described preferredembodiments the recommended procedures are for cryoablation of tissuesof a prostate.

According to still further features in the described preferredembodiments the recommended procedures are for treating BPH,percutaneously or transperineally.

According to still further features in the described preferredembodiments the recommended procedures are for treating a mass.

According to still further features in the described preferredembodiments the recommended procedures are for treating a malignancy.

According to still further features in the described preferredembodiments the table comprises a measure of volume of a prostate.

According to still further features in the described preferredembodiments the table comprises a measure of length of a stricture of aurethra.

According to still further features in the described preferredembodiments the table comprises a measure of symptomatic severity of aBPH condition.

According to still further features in the described preferredembodiments the measure of symptomatic severity of a BPH condition is anAUA score.

According to still further features in the described preferredembodiments the recommendation is of multiple cryoprobes closely placedso as to ensure a continuous cold field sufficient to ensure completedestruction of tissues within a target volume, while minimizing damageto tissues outside the target volume.

According to still another aspect of the present invention there isprovided a method for facilitating a cryosurgery ablation procedure,comprising utilizing a first imaging modality for creating digitizedpreparatory images of an intervention site, utilizing athree-dimensional modeler for creating a first three-dimensional modelof the intervention site based on the digitized preparatory images,utilizing a second imaging modality for creating a digitized real-timeimage of at least a portion of the intervention site during acryosurgery procedure, and utilizing an images integrator forintegrating information from the three-dimensional model of the site andfrom the real-time image of the site in a common coordinate system,thereby producing an integrated image the site, facilitative to anoperator practicing a cryoablation procedure.

According to still further features in the described preferredembodiments the method further comprises utilizing a planning method.

According to still further features in the described preferredembodiments the method further comprises utilizing a displayer fordisplaying the integrated image in a common virtual space.

According to still further features in the described preferredembodiments the displayed integrated image is a two-dimensional image.

According to still further features in the described preferredembodiments the displayed integrated image is a three-dimensional image.

According to still further features in the described preferredembodiments the method further comprises utilizing a three-dimensionalmodeler for creating a second three-dimensional model of at least aportion of the intervention site based on a plurality of real-timeimages.

According to still further features in the described preferredembodiments he method further comprises utilizing the images integratorto integrate information from the first three-dimensional model of thesite and from the second three-dimensional model of at least a portionof the site in a common coordinate system.

According to still further features in the described preferredembodiments the first imaging modality comprises at least one of a groupcomprising magnetic resonance imaging, ultrasound imaging, andcomputerized tomography imaging.

According to still further features in the described preferredembodiments the second imaging modality comprises at least one of agroup comprising magnetic resonance imaging, ultrasound imaging, andcomputerized tomography imaging.

According to still further features in the described preferredembodiments the method further comprises utilizing an imaging tool toreport a position of the tool during creation of the real-time image,thereby providing localizing information about the real-time imageuseable by the images integrator.

According to still further features in the described preferredembodiments the imaging tool is an ultrasound probe inserted in therectum of a patient operated to report a distance of penetration of thetool in the rectum of the patient during creation of ultrasound imagesof a prostate of the patient.

According to still further features in the described preferredembodiments the first three-dimensional model is expressed in athree-dimensional Cartesian coordinate system.

According to still further features in the described preferredembodiments the method further comprises utilizing an interface tohighlight selected regions within the first three-dimensional model.

According to still further features in the described preferredembodiments the integrated image comprises a display of anoperator-highlighted region.

According to still further features in the described preferredembodiments the method further comprises utilizing the interface foridentifying tissues to be cryoablated.

According to still further features in the described preferredembodiments the integrated image further comprises a display of theoperator-identified tissues to be cryoablated.

According to still further features in the described preferredembodiments he method further comprises utilizing the interface foridentifying tissues to be protected from damage during cryoablation.

According to still further features in the described preferredembodiments the integrated image further comprises a display of theoperator-identified tissues to be protected from damage during thecryoablation.

According to still further features in the described preferredembodiments the method further comprises utilizing the interface forlabeling topographic features of the first three-dimensional model.

According to still further features in the described preferredembodiments the method further comprises utilizing the interface forlabeling topographic features of the real-time images.

According to still further features in the described preferredembodiments the method further comprises utilizing the interface forlabeling topographic features of the second three-dimensional model.

According to still further features in the described preferredembodiments the images integrator matches operator-labeled topographicfeatures of the first three-dimensional model with operator-labeledfeatures of the real-time images, to orient the first three-dimensionalmodel and the real-time image with respect to the common coordinatesystem.

According to still further features in the described preferredembodiments the images integrator matches operator-labeled topographicfeatures of the first three-dimensional model with operator-labeledfeatures of the second three-dimensional model, to orient the firstthree-dimensional model and second three-dimensional model with respectto the common coordinate system.

According to still further features in the described preferredembodiments the method further comprises simulating a cryosurgicalintervention by utilizing a simulator having an interface, and utilizingthe interface during a planning phase of the intervention to specifyloci for insertion of cryoprobes into a cryoablation site in a patientand to specify operational parameters for operation of the cryoprobesfor cryoablating tissues, and further utilizing the image integrator tointegrate the specified loci into the integrated image, and utilizingthe displayer to display the integrated image.

According to still further features in the described preferredembodiments the method further comprises simulating a cryosurgicalintervention by receiving from an operator during a planning phase ofthe intervention specifications of loci for insertion of cryoprobes intoa cryoablation site and operational parameters for operation of thecryoprobes for cryoablating tissues, utilizing the image integrator tointegrate the operator-specified loci into the integrated image, andutilizing the displayer to display the integrated image.

According to still further features in the described preferredembodiments the method further comprises utilizing a first comparatorfor comparing the first three-dimensional model with the real-time imageto determine differences.

According to still further features in the described preferredembodiments the method further comprises utilizing apparatus forproviding feedback to an operator regarding position of tools being usedduring a surgical intervention as compared to the loci for insertion ofcryoprobes specified by an operator during the planning phase of theintervention.

According to still further features in the described preferredembodiments the method further comprises providing feedback to anoperator regarding a position of a tool being used during a surgicalintervention as compared to the loci for insertion of cryoprobesspecified by an operator during the planning phase of the intervention.

According to still further features in the described preferredembodiments the method further comprises utilizing apparatus forproviding feedback to an operator regarding a position of a tool beingused during a surgical intervention as compared to a position ofoperator-identified tissues to be cryoablated.

According to still further features in the described preferredembodiments the method further comprises utilizing apparatus forproviding feedback to an operator regarding a position of a tool beingused during a surgical intervention as compared to a position ofoperator-identified tissues to be protected during cryoablation.

According to still further features in the described preferredembodiments the method further comprises utilizing apparatus for guidingan operator in the placement of cryoprobes for affecting cryoablation,the guiding being according to the loci for insertion of cryoprobesspecified by an operating during the planning phase of the intervention.

According to still further features in the described preferredembodiments the method further comprises guiding an operator in theplacement of cryoprobes for affecting cryoablation, the guiding beingaccording to the loci for insertion of cryoprobes specified by anoperating during the planning phase of the intervention.

According to still further features in the described preferredembodiments the method further comprises utilizing apparatus forlimiting movement of a cryoprobe during a cryoablation intervention, thelimitation being according to the loci for insertion of cryoprobesspecified by an operating during the planning phase of the intervention.

According to still further features in the described preferredembodiments the method further comprises utilizing cryoprobedisplacement apparatus for moving at least one cryoprobe to at least oneof the loci for insertion of cryoprobes specified by an operator duringthe planning phase of the intervention.

According to still further features in the described preferredembodiments the method further comprises utilizing a stepper motor tomove the cryoprobe.

According to still further features in the described preferredembodiments the method further comprises utilizing a position sensor tosense a position of the cryoprobe.

According to still further features in the described preferredembodiments the method further comprises utilizing control apparatus tocontrol cooling of the at least one cryoprobe.

According to still further features in the described preferredembodiments the method further comprises utilizing control apparatus tocontrol heating of the at least one cryoprobe.

According to still further features in the described preferredembodiments the method further comprises controlling the at least onecryoprobe according to a schedule of movements coordinated with aschedule of alternative heating and cooling of the at least onecryoprobe, to affect cryoablation at a plurality of loci.

The present invention successfully addresses the shortcomings of thepresently known configurations by providing a system and method foreffectively planning a cryoablation procedure by simulating such aprocedure based on preparatory imaging of a target site in a patient, bysimulating the procedure, by recommending procedural steps and byevaluating procedural steps specified by a user.

The present invention further successfully addresses the shortcomings ofthe presently known configurations by providing a system and method forfacilitating a cryoablation intervention by relating preparatory imagingof a site, and plans for intervening at that site, to real-time imagesof the site during cryoablation.

The present invention further successfully addresses the shortcomings ofthe presently known configurations by providing a system and method forcompletely destroying target tissues at a cryoablation site whilelimiting damage to healthy tissues in close proximity to that site.

Implementation of the method and the apparatus of the present inventioninvolves performing or completing selected tasks or steps manually,automatically, or a combination thereof. Moreover, according to actualinstrumentation and equipment of preferred embodiments of the method andapparatus of the present invention, several selected steps could beimplemented by hardware or by software on any operating system of anyfirmware or a combination thereof. For example, as hardware, control ofselected steps of the invention could be implemented as a chip or acircuit. As software, control of selected steps of the invention couldbe implemented as a plurality of software instructions being executed bya computer using any suitable operating system. In any case, selectedsteps of the method of the invention could be described as beingcontrolled by a data processor, such as a computing platform forexecuting a plurality of instructions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the present invention only, and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the invention. In this regard, no attempt is made to show structuraldetails of the invention in more detail than is necessary for afundamental understanding of the invention, the description taken withthe drawings making apparent to those skilled in the art how the severalforms of the invention may be embodied in practice.

In the drawings:

FIG. 1 a is a graph showing the profile of temperature distributionwithin an ice-ball formed at the tip of a cryosurgical probe;

FIG. 1 b is a graph showing the effectiveness of a cryosurgicaltreatment, given in percentage of tissue destruction, as a function oftemperature;

FIGS. 2 a-2 c are cross sectional views of an ice-ball formed at the tipof a conventional cryosurgical probe introduced into a patient'sprostate;

FIGS. 3 a-3 b are cross sectional views of two ice-balls formed at thetips of cryosurgical probes introduced into a patient's prostate,according to methods of the prior art;

FIG. 4 is a cross sectional view illustrating a method for treating apatient's prostate, according to methods of the prior art;

FIG. 5 is a cross sectional view illustrating a further method fortreating a patient's prostate, according to methods of the prior art;

FIG. 6 a is a schematic illustration of a multi-probe cryosurgicaldevice according to methods of the prior art;

FIG. 6 b is a schematic illustration of a pre-cooling element accordingto methods of the prior art;

FIG. 7 is a schematic longitudinal section of a preferred cryosurgicalprobe according to methods of the prior art;

FIG. 8 is a perspective view of a guiding element for receivingcryosurgical probes, the guiding element being connected to anultrasound probe, according to methods of the prior art;

FIGS. 9 and 10 illustrate a method including the steps of forming athree-dimensional grid of a patient's prostate and introducingcryosurgical probes thereto, according to methods of the prior art;

FIG. 11 is a simplified block diagram of a planning system for planninga cryoablation procedure, according to a first preferred embodiment ofthe present invention;

FIGS. 12 a-12 b are a flow chart showing a method for automaticallygenerating a recommendation relating to a cryoablation procedure,according to an embodiment of the present invention;

FIG. 13 is a chart showing temperature profiles for several cryoablationmethods, is useful for understanding FIGS. 14 and 15;

FIG. 14 is a simplified flow chart showing a method for ensuring totaldestruction of a selected volume while limiting damage to tissuesoutside that selected volume, according to an embodiment of the presentinvention;

FIG. 15 is a simplified flow chart showing another method for ensuringtotal destruction of a selected volume while limiting damage to tissuesoutside that selected volume, according to an embodiment of the presentinvention;

FIG. 16 is a simplified block diagram of surgical facilitation systemfor facilitating a cryosurgery ablation procedure, according to anembodiment of the present invention; and

FIG. 17 is a schematic diagram of mechanisms for control of cryosurgicaltools by a surgical facilitation system, according to an embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to system and method for planning acryoablation procedure and to system and method for facilitating acryoablation procedure. More particularly, the present invention relatesto the use of integrated images displaying, in a common virtual space, athree-dimensional model of a surgical intervention site based ondigitized preparatory images of the site from first imaging modalities,simulation images of cryoprobes used according to an operator-plannedcryoablation procedure at the site, and real-time images provided bysecond imaging modalities during cryoablation. The present inventionfurther relates to system-supplied recommendations for and evaluationsof the planned cryoablation procedure, and to system-supplied feedbackto an operator and system-supplied guidance and control signals foroperating a cryosurgery tool during cryoablation. The present inventionstill further relates to methods for generating a nearly-uniform coldfield among a plurality of cryoprobes, for cryoablating a volume withsmooth and well-defined borders.

For purposes of better understanding the present invention, reference isfirst made to the construction and operation of conventional (i.e.,prior art) systems as illustrated in FIGS. 1-10.

FIG. 1 a illustrates the profile of temperature distribution across anice-ball formed at the tip of a cryosurgical probe. As shown, thetemperature at a surface 5 of the ice-ball is 0° C. The temperaturedeclines exponentially towards a center 1 of the ball where itpreferably reaches the value of −170° C., such that an isothermalsurface 7 of about −40° C. is typically located within the ice-ball atthe half way between the center of the ball and its surface. Thus, ifthe ice-ball features a radius R, then the radius of the −40° C.isothermal surface 7 is about R/2.

FIG. 1 b is a graph showing the effectiveness of a cryosurgicaltreatment (given in percentage of tissue destruction) as a function oftemperature. As shown, the temperature required for effectivelydestroying a tissue is at least about −40° C. Accordingly, in order toeffectively destroy a tissue, the isothermal surface of −4° C. (shown inFIG. 1 a) should be placed at the periphery of the treated tissue sothat the entire area of the treated tissue is exposed to at least about−40° C., thereby exposing adjacent healthy tissues and organs to theexternal portion of the ice-ball. The application of temperatures ofbetween about −40° C. and 0° C. to such healthy tissues usually causessubstantial damage thereto, which damage may result in temporary orpermanent impairment of functional organs.

FIGS. 2 a-2 c illustrate prior-art cryosurgical methods wherein a singlecryosurgical probe of a substantially large diameter, typically 3-5millimeters, is introduced between the patient's prostatic urethra andthe periphery of the prostate, so as to destroy the prostatic tissueextending therebetween.

Specifically, FIGS. 2 a-2 c are cross sectional views of an ice-ball 9formed at the end of a conventional cryosurgical tip introduced into aprostate 2 of a patient. The patient's prostatic urethra, rectum andnerves are designated as 4, 3, and 6 respectively.

A single ice-ball 9 is formed within the prostatic tissue segmentextending between the prostatic urethra 4 and the periphery of theprostate 13. The dimensions of a conventional cryosurgical probe aredesigned so as to provide an ice-ball 9 having an inner portion 10extending through a substantially significant portion of such a tissuesegment, so as to apply temperatures of between about −170° C. and about−40° C. thereto. The application of a single probe for producing asingle ice-ball 9 imposes a trade-off between several options.

FIGS. 2 a and 2 b illustrate the trade-off between a first option ofavoiding the damaging of the patient's prostatic urethra 4 yet damagingnerves 6 present close to the periphery 13 of the prostate 2 (FIG. 2 a),and a second option of avoiding the damaging of the patient's nerves 6yet damaging urethra 4 (FIG. 2 b).

As shown in FIG. 2 a, the isothermal surface 7 of −40° C. is positionedsubstantially at the periphery 13 of the patient's prostate 2, such thatsurface 5 of the ice-ball 9 is positioned substantially near thepatient's urethra 4, so as to avoid damaging of the patient's urethra 4.Thus, the inner portion 10 of ice-ball 9 effectively freezes theperipheral regions (in cross section) of the prostate, while outerportion 12 of ice-ball 9 extends through the patient's nerves 6. Theapplication of temperatures of between about −40° C. and 0° C. to thepatient's nerves 6 may result in temporary or permanent impairmentthereof.

Similarly, when ice-ball 9 is positioned between the patient's urethra 4and rectum 3 in such a manner so as to avoid the damaging of urethra 4,the application of between about −40° C. and 0° C. to the patient'srectum may result in temporary or permanent impairment thereof.

As shown in FIG. 2 b, the isothermal surface 7 of −40° C. is positionedsubstantially near the patient's urethra 4 such that surface 5 ofice-ball 9 is positioned substantially near the patient's nerves 6and/or rectum 3 (not shown), so as to avoid damaging of the patient'snerves 6 and/or rectum 3. Thus, inner portion 10 of ice-ball 9effectively freezes the central regions (in cross section) of prostate2, while outer portion 12 of ice-ball 9 extends through the patient'surethra 4. The application of temperatures of between about −40° C. and0° C. to the patient's urethra 4 may result in temporary or permanentimpairment thereof.

However, none of the alternatives shown in FIGS. 2 a and 2 b provides aneffective treatment (temperature of at least about −40° C.) to theentire prostatic tissue segment extending between urethra 4 and theperiphery 13 of the prostate, thereby exposing the patient to the riskof malignancy.

FIG. 2 c shows another possible alternative wherein a thickercryosurgical probe, having a tip diameter of between 4 and 6 millimetersis used for producing a lager ice-ball, of about 4-5 centimeters indiameter, so as to enable effective treatment of the entire prostatictissue segment extending between the urethra 4 and periphery 13 ofprostate 2. As shown, inner portion 10 of the ice-ball 9 extends throughthe entire tissue segment (in cross section) between urethra 4 andperiphery 13 of the prostate, thereby exposing urethra 4 and nerves (notshown), as well as the rectum 3, to outer portion 12 of the ice-ball 9.

The thickness (in cross section) of tissues exposed to outer portion 12of the ice-ball is about R/2, wherein R is the radius of ice-ball 9.Thus, the volume of adjacent tissues exposed to damage becomessubstantially greater than the volume of the treated tissue.

Thus, the conventional cryosurgical probes and methods fail to providethe necessary resolution of treatment required for enabling an accurateand effective destruction of a tissue while preserving other tissues andorgans adjacent thereto.

FIGS. 3 a and 3 b are schematic illustrations of a cryosurgical methodaccording to another method of prior art, wherein a plurality ofcryosurgical probes of substantially small diameters are introducedbetween the patient's prostatic urethra 4 and periphery 13 of prostate2, so as to destroy the prostatic tissue extending therebetween.

As shown in FIG. 3 a, preferably two probes are introduced into aprostatic tissue segment extending between the patient's prostaticurethra 4 and periphery 13 of prostate 2, so as to form two smallerice-balls, 9 a and 9 b.

According to the configuration shown in FIG. 3 a, each of ice-balls 9 aand 9 b features a radius of R/2, which is half the radius of ice-ball 9shown in FIG. 2 c. Accordingly, ice-balls 9 a and 9 b include respectiveinner portions, 14 a and 14 b, each having a radius of R/4, andrespective outer portions, 16 a and 16 b, each having a thickness ofR/4.

Therefore, by introducing two probes of a small diameters rather than asingle probe of a larger diameter into the tissue segment extendingbetween prostatic urethra 4 and periphery 13 of prostate 2, thethickness of adjacent tissues exposed to damage is substantiallydecreased. The specific example of FIG. 3 a shows that the thickness (incross section) of adjacent tissues exposed to between about −40° C. and0° C. is only R/4, which is half the thickness and respectively muchless the volume (e.g., 8 fold less), exposed to damage when using theprior art method (shown in FIG. 2 c).

By further decreasing the diameter of the cryosurgical probes andintroducing a plurality of probes into the tissue segment extendingbetween urethra 4 and periphery 13 of prostate 2, the damage tosurrounding tissues may be further minimized, thereby improving theresolution of the cryosurgical treatment.

Another prior art embodiment is shown in FIG. 3 b, wherein two probesare introduced into the tissue segment extending between the patient'surethra 4 and periphery 13 of prostate 2, so as to form two ice-balls 9a and 9 b, such that inner portion 14 a of ice-ball 9 a is substantiallyspaced from inner portion 14 b of ice-ball 9 b, and outer portion 16 aof ice-ball 9 a partially overlaps outer portion 16 b of ice-ball 9 b,the overlapping region being designated as 17. The specific exampleshown in FIG. 3 b is of two ice-balls each having a radius of R/5,wherein R is the radius of a conventional ice-ball as shown in FIG. 2 c.By using such configuration, the thickness of adjacent tissues exposedto damage is decreased to R/5 and the volume thereof is decreasedrespectively. It will be appreciated that in the example givensubstantial fractions of region 17, from which heat is extracted by twoprobes, will become cooler than −40° C.

The specific examples shown in FIGS. 3 a and 3 b are of two ice-ballshaving tangent and spaced inner portions, respectively. However, aplurality of probes may be used, each having a distinct diameter, theinner portions of which being tangent or spaced.

Referring to FIG. 4, a prior-art cryosurgical method is shown,illustrating the distribution of a plurality of cryosurgical probesacross a patient's prostate, wherein a single probe is introduce into atissue segment extending between prostatic urethra 4 and periphery 13 ofprostate 2. According to such a prior art method, about 5-7 probes areintroduced into the patient's prostate, wherein each of the probesfeatures a diameter of about 3 millimeters. FIG. 4 shows a specificexample wherein five probes are introduced so as to form five ice-ballshaving inner portions 10 a-10 e and outer portions 12 a-12 e. As shown,an effective treatment is provided by inner portions 10 a-10 e, andregions therebetween marked 19, only to limited regions of the prostate,wherein the damage caused to adjacent tissues such as the patient'surethra 4, rectum 3 and nerve 6 b by outer portions 12 a-12 e isconsiderable.

FIG. 5 shows a preferred distribution of cryosurgical probes accordingto another method of prior art. As shown, at least two cryosurgicalprobes of substantially small diameter are introduced into specificsegments of prostatic tissue extending between urethra 4 and periphery13 of prostate 2. FIG. 5 shows a specific example wherein twenty probesare introduced into the patient's prostate 2, including five pairs ofinner and outer cryosurgical probes located at specific segments of theprostate extending from the urethra 4 to periphery 13, and additional(five pairs in the example given) of outer cryosurgical probes areintroduced therebetween. The inner portions of the ice-balls formed bythe pairs of outer and inner probes are designated as 14 a and 14 b,respectively, wherein the inner portions of the ice-balls formedtherebetween are designated as 14 c.

The diameter of a single cryosurgical probe according to the prior artmethod presented in FIG. 5 is preferably between about 1.2 millimetersand about 1.4 millimeters.

As shown, such distribution of substantially small diameter cryosurgicalprobes enables to provide an effective treatment of at least −40° C. toa larger area of the prostatic tissue while substantially minimizing thethickness of healthy adjacent tissues exposed to damage.

Thus, the prior art method presented in FIG. 5 substantially increasesthe effectiveness and resolution of treatment relative to the prior artmethod presented by FIG. 4.

The pattern of distribution of probes shown in FIG. 5 includes an innercircle and an outer circle of probes, wherein a portion of the probes isarranged in pairs of an inner probe and an outer probe. According toanother configuration (not shown), the probes are arranged in an innercircle and an outer circle, but not necessarily in pairs of an innerprobe and an outer probe.

The probes may be sequentially introduced to and extracted from thepatient's prostate so as to sequentially freeze selected portionsthereof. A method of quick extraction of the probes without tearingpieces of tissue from the patient, which stick to the tip of the probe,is disclosed hereinunder.

The introduction of a plurality of small diameter cryosurgical probesimproves the resolution of treatment along the planes perpendicular tothe axis of penetration of the probes into the prostate. However, theprostate, as other anatomical organs, features an asymmetric threedimensional shape. Thus, a specific pattern of distribution of probesmay provide an effective treatment to a distinct plane located at aspecific depth of penetration, but at the same time may severely damagenon-prostatic tissues located at other depths of penetration. There isneed for cryosurgical method and apparatus which enable high resolutionof treatment along and perpendicular to the axis of penetration of theprobes into a patient's organ. Presented hereinbelow is a cryosurgicalmethod and apparatus according to prior art which enable high resolutionof treatment along the axis of penetration of the cryosurgical probeinto the patient's organ as well as along the planes perpendicular tothe axis of penetration, wherein these high resolutions are achieved byforming a three-dimensional grid of the organ, preferably by usingultrasound imaging, and inserting each of the cryosurgical probes to aspecific depth within the organ according to the information provided bythe grid.

Referring to FIGS. 6 a, 6 b and 7, a cryosurgical apparatus according tomethods of prior art includes a plurality of cryosurgical probes 53,each having an operating tip 52 including a Joule-Thomson cooler forfreezing a patient's tissue and a holding member 50 for holding by asurgeon. As shown in FIG. 7, operating tip 52 includes at least onepassageway 78 extending therethrough for providing gas of high pressureto orifice 80 located at the end of operating tip 52, orifice 80 beingfor passage of high pressure gas therethrough, so as to cool operatingtip 52 and produce an ice-ball at its end 90. Gases which may be usedfor cooling include, but are not limited to argon, nitrogen, air,krypton, CO₂, CF₄, xenon, or N₂O.

When a high pressure gas such as argon expands through orifice 80 itliquefies, so as to form a cryogenic pool within chamber 82 of operatingtip 52, which cryogenic pool effectively cools surface 84 of operatingtip 52. Surface 84 of operating tip 52 is preferably made of a heatconducting material such as metal so as to enable the formation of anice-ball at end 90 thereof.

Alternatively, a high pressure gas such as helium may be used forheating operating tip 52 via a reverse Joule-Thomson process, so as toenable treatment by cycles of cooling-heating, and further forpreventing sticking of the probe to the tissue when extracted from thepatient's body, and to enable fast extraction when so desired.

When a high pressure gas such as helium expands through orifice 80 itheats chamber 82, thereby heating surface 84 of operating tip 52.

Operating tip 52 includes at least one evacuating passageway 96extending therethrough for evacuating gas from operating tip 52 to theatmosphere.

As shown FIG. 7, holding member 72 may include a heat exchanger forpre-cooling the gas flowing through passageway 78. Specifically, theupper portion of passageway 78 may be in the form of a spiral tube 76wrapped around evacuating passageway 96, the spiral tube beingaccommodated within a chamber 98. Thus, gas evacuated through passageway96 may pre-cool the incoming gas flowing through spiral tube 76.

As further shown in FIG. 7, holding member 72 may include an insulatingbody 92 for thermally insulating the heat exchanger from the externalenvironment.

Furthermore, operating tip 52 may include at least one thermal sensor 87for sensing the temperature within chamber 82, the wire 89 of whichextending through evacuating passageway 96 or a dedicated passageway(not shown).

In addition, holding member 72 may include a plurality of switches 99for manually controlling the operation of probe 53 by a surgeon. Suchswitches may provide functions such as on/off, heating, cooling, andpredetermined cycles of heating and cooling by selectively andcontrollably communicating incoming passageway 70 with an appropriateexternal gas container including a cooling or a heating gas.

As shown in FIG. 6 a, each of cryosurgical probes 53 is connected via aflexible connecting line 54 to a connecting site 56 on a housing element58, preferably by means of a linking element 51. Cryosurgical probes 53may be detachably connected to connecting sites 56.

Preferably, evacuating passageway 96 extends through connecting line 54,such that the outgoing gas is evacuated through an opening located atlinking element 51 or at any other suitable location, e.g., manifold 55,see below. Preferably, line 54 further includes electrical wires forproviding electrical signals to the thermal sensor and switches (notshown).

Each of cryosurgical probes 53 is in fluid communication with a manifold55 received within a housing 58, manifold 55 being for distributing theincoming high pressure gas via lines 57 to cryosurgical probes 53.

As shown, housing 58 is connected to a connector 62 via a flexible cable60 including a gas tube (not shown), connector 62 being for connectingthe apparatus to a high pressure gas source and an electrical source.

The apparatus further includes electrical wires (not shown) extendingthrough cable 60 and housing 58 for providing electrical communicationbetween the electrical source and cryosurgical probes 53.

Preferably, housing 58 includes a pre-cooling element, generallydesignated as 61, for pre-cooling the high pressure gas flowing tocryosurgical probes 53. Preferably, pre-cooling element 61 is aJoule-Thomson cooler, including a tubular member 48 received within achamber 49, tubular member 48 including an orifice 59 for passage ofhigh pressure gas therethrough, so as to cool chamber 49, therebycooling the gas flowing through tubular member 48 into manifold 55.

Another configuration of a pre-cooling element 61 is shown in FIG. 6 b,wherein tubular member 48 is in the form of a spiral tube wrapped arounda cylindrical element 47, so as to increase the area of contact betweentubular member 48 and the cooling gas in chamber 49.

According to yet another configuration (not shown), housing 58 includesa first tubular member for supplying a first high pressure gas tomanifold 55, and a second tubular member for supplying a second highpressure gas to pre-cooling element 61. Any combination of gases may beused for cooling and/or heating the gases flowing through such tubularmembers.

Alternatively, a cryogenic fluid such as liquid nitrogen may be used forpre-cooling the gas flowing through housing 58. Alternatively, anelectrical pre-cooling element may used for pre-cooling the gas.

Preferably, thermal sensors (not shown) may be located within cable 60and manifold 55 for measuring the temperature of gas flowingtherethrough.

Referring to FIGS. 8-10, method and apparatus according to prior artapplies an imaging device such as ultrasound, MRI or CT, so as to form athree-dimensional grid of the patient's treated organ, e.g., prostate,the three dimensional grid serves for providing information on the threedimensional shape of the organ. Each of the cryosurgical probes is theninserted to a specific depth within the organ according to theinformation provided by the grid.

As shown in FIG. 8, an ultrasound probe 130 is provided for insertioninto the patient's rectum, ultrasound probe 130 being received within ahousing element 128. A guiding element 115 is connected to housingelement 128 by means of a connecting arm 126. As shown, guiding element115 is in the form of a plate 110 having a net of apertures 120, eachaperture serves for insertion of a cryosurgical probe therethrough.Preferably, the distance between each pair of adjacent apertures 120 isbetween about 2 millimeters and about 5 millimeters.

As shown in FIG. 9, ultrasound probe 130 is introduced to a specificdepth 113 within the patient's rectum 3. A net of marks 112 is providedon the obtained ultrasound image 114, the net of marks 112 on image 114being accurately correlated to the net of apertures 120 on guidingelement 115.

Thus, marks 112 on image 114 sign the exact locations of the centers ofice-balls which may be formed at the end of the cryosurgical probesinserted through apertures 120 to the patient's prostate 2, whereinimage 114 relates to a specific depth of penetration 113 of thecryosurgical probes into the prostate 2.

As shown in FIG. 9, ultrasound probe 130 is gradually introduced tovarious depths 113 of rectum 3, thereby producing a set of images 114,wherein each image relates to a respective depth of penetration into theprostate 2. Thus, each of images 114 relates to a specific planeperpendicular to the axis of penetration of the cryosurgical probes.

The set of images 114 provides a three dimensional grid of the prostate.Such three-dimensional grid is then used for planning the cryosurgicalprocedure.

For example, the introduction of a cryosurgical probe along a given axisof penetration to a first depth may effectively destroy a prostatictissue segment, while introduction of the probe to a second depth mayseverely damage the prostatic urethra.

Since the ice-ball is locally formed at the end of the cryosurgicalprobe, each probe may be introduced to a specific depth so as to locallyprovide an effective treatment to a limited portion of the prostatewhile avoiding the damaging of non-prostatic or prostatic tissueslocated at other depths of penetration.

FIG. 10 shows the insertion of an operating tip 52 of a cryosurgicalprobe 50 through an aperture of guiding element 115 into the prostate 2of a patient.

Preferably, a plurality of cryosurgical probes are sequentially insertedthrough apertures 120 of guiding element 115 into the patient'sprostate, wherein each probe is introduced to a specific depth, therebyproviding substantially local effective treatment to distinct segmentsof the prostatic tissue while avoiding the damaging of other prostaticor nonprostatic tissue segments.

Preferably, each of the cryosurgical probes includes a scale forindicating the depth of penetration into the prostate.

Reference is now made to FIG. 11, which is a simplified block diagram ofa planning system for planning a cryoablation procedure, according to afirst preferred embodiment of the present invention.

In FIG. 11, a planning system 240 for planning a cryoablation procedurecomprises a first imaging modality 250 which serves for creatingdigitized preparatory images 254 of a cryoablation intervention site.First imaging modality 250 will typically be a magnetic resonanceimaging system (MRI), an ultrasound imaging system, a computerizedtomography imaging system (CT), a combination of these systems, or asimilar system able to produce images of the internal tissues andstructures of the body of a patient. First imaging modality 250 is forproducing digitized images of a cryoablation intervention site, whichsite includes body tissues whose cryoablation is desired (referred toherein as “target” tissue), which may be a tumor or other structure, andbody tissues and structures in the immediate neighborhood of the targettissues, which constitute the target tissue's physical environment.

Some types of equipment useable as first imaging modality 250, a CTsystem for example, typically produce a digitized image in acomputer-readable format. If equipment used as first imaging modality250 does not intrinsically produce digitized output, as might be thecase for conventional x-ray imaging, then an optional digitizer 252 maybe used to digitize non-digital images, to produce digitized preparatoryimages 254 of the site.

Digitized images 254 produced by first imaging modality 250 and optionaldigitizer 252 are passed to a three-dimensional modeler 256 for creatinga three-dimensional model 258 of the intervention site. Techniques forcreating a three dimensional model based on a set of two dimensionalimages are well known in the art. In the case of CT imaging, creation ofa three dimensional model is typically an intrinsic part of the imagingprocess. PROVISION, from Algotec Inc.(http://www.algotec.com/products/provision.htm) is an example ofsoftware designed to make a 2-D to 3-D conversion for images generatedby CT scans. To accomplish the same purpose starting from ultrasoundimaging, SONOReal™ software from BIOMEDICOM (http://www.biomedicom.com/)may be used.

Three dimensional model 258 is preferably expressible in a threedimensional Cartesian coordinate system.

Three dimensional model 258 is useable by a simulator 260 for simulatinga cryosurgical intervention. Simulator 260 comprises a displayer 262 fordisplaying views of model 258, and an interface 264 useable by anoperator for specifying loci for insertion of simulated cryoprobes 266and operational parameters for operation of simulated cryoprobes 266 forcryoablating tissues. Thus, an operator (i.e., a user) can use simulator260 to simulate a cryoablation intervention, by using interface 264 tocommand particular views of model 258, and by specifying both where toinsert simulated cryoprobes 266 into an organ imaged by model 258, andhow to operate cryoprobes 266. Typically, an operator may specifypositions for a plurality of simulated cryoprobes 266, and furtherspecify operating temperatures and durations of cooling for cryoprobes266. Display 262 is then useable for displaying in a common virtualspace an integrated image 268 comprising a display of three dimensionalmodel 258 and a virtual display of simulated cryoprobes 266 inserted atsaid operator-specified loci.

Planning system 240 optionally comprises a memory 270, such as acomputer disk, for storing operator-specified loci for insertion ofcryoprobes and operator-specified parameters for operation simulatedcryoprobes 266.

Interface 264 comprises a highlighter 280 for highlighting, undercontrol of an operator, selected regions within three dimensional model258. Operator-highlighted selected regions of model 258 are thenoptionally displayed as part of an integrated image 268.

In particular, highlighter 280 is useable by an operator for identifyingtissues to be cryoablated. Preferably, interface 264 permits an operatorto highlight selected regions of three dimensional model 258 so as tospecify therein tissues to be cryoablated, or alternatively interface264 permits an operator to highlight selected regions of digitizedpreparatory images 254, specifying therein tissues to be cryoablated. Inthe latter case, three-dimensional modeler 256 is then useable totranslate regions highlighted on digitized preparatory images 254 intoequivalent regions of three dimensional model 258. In both cases,tissues highlighted and selected to be cryoablated can be displayed bydisplayer 262 as part of integrated image 268, and can be recorded bymemory 270 for future display or other uses.

Similarly, highlighter 280 is useable by an operator for identifyingtissues to be protected from damage during cryoablation. Typically,important functional organs not themselves involved in pathology may bein close proximity to tumors or other structures whose destruction isdesired. For example, in the case of cryoablation in a prostate, nervebundles, the urethra, and the rectum may be in close proximity totissues whose cryoablation is desired. Thus, highlighter 280 is useableby an operator to identify (i.e., to specify the location of) suchtissues and to mark them as requiring protection from damage duringcryoablation.

Preferably, interface 264 permits an operator to highlight selectedregions of three dimensional model 258 so as to specify therein tissuesto be protected from damage during cryoablation. Alternatively,interface 264 permits an operator to highlight selected regions ofdigitized preparatory images 254, specifying therein tissues to beprotected during cryoablation. In the latter case, three-dimensionalmodeler 256 is then useable to translate regions highlighted ondigitized preparatory images 254 into equivalent regions of threedimensional model 258. In both cases, tissues highlighted and selectedto be protected from damage during cryoablation can be displayed bydisplayer 262 as part of integrated image 268, and can be recorded bymemory 270 for future display or other uses.

Planning system 240 further optionally comprises a predictor 290, anevaluator 300, and a recommender 310.

Predictor 290 serves for predicting the effect on tissues of a patient,if a planned operation of cryoprobes 266 at the operator-specified lociis actually carried out according to the operator-specified operationalparameters. Predictions generated by predictor 290 may optionally bedisplayed by displayer 262 as part of integrated image 268, in thecommon virtual space of image 268.

In a preferred embodiment, predictions of predictor 290 are based onseveral sources. The laws of physics, as pertaining to transfer of heat,provide one predictive source. Methods of calculation well known in theart may be used to calculate, with respect to any selected region withinthree dimensional model 258, a predicted temperature, given knownlocations of cryoprobes 266 which are sources of cooling in proximity tosuch a region, known temperatures and cooling capacities of cryoprobes266, and a duration of time during which cryoprobes 266 are active incooling. Thus, a mathematical model based on known physical laws allowsto calculate a predicted temperature for any selected region withinmodel 258 under operator-specified conditions.

Experimentation and empirical observation in some cases indicate a needfor modifications of a simple mathematical model based on physical lawsconcerning the transfer of heat, as would be the case, for example, in atissue wherein cooling processes were modified by a high rate of bloodflow. However, methods for adapting such a model to such conditions arealso well known in the art. Such methods take into account heatdissipation in flowing systems, effected by the flow.

An additional basis for predictions of predictor 290 is that of clinicalobservation over time. Table 1 provides an example of a predictive basisderived from clinical observation, relating to medium-term and long-termeffects of cryoablation procedures in a prostate. The example providedin Table 1 relates to treatment of BPH by cryoablation under astandardized set of cryoprobe operating parameters.

TABLE 1 Predicted long-term effects of cryoablation Distance between 3week volume 3 months volume probes (mm) consumption (%) consumption (%)10 70 100 15 55 85 20 40 70 25 30 50

As may be seen from Table 1, clinical observation leads to theconclusion that reduction in the volume of a prostate followingcryoablation is a gradual process which continues progressively for anumber of weeks following a cryoablation procedure. The clinicallyderived information of Table 1, and similar clinically derivedinformation, can also serve as a basis for predictions generated bypredictor 290, and displayed by displayer 262 as part of integratedimage 268 in the common virtual space of image 268.

Evaluator 300 is useable to compare results predicted by predictor 290to goals of a surgical intervention as expressed by an operator. Inparticular, evaluator 300 can be used to compare intervention resultspredicted by predictor 290 under a given intervention plan specified byan operator, with that operator's specification of tissues to becryoablated. Thus, an operator may use interface 264 to specify tissuesto be cryoablated, plan an intervention by using interface 264 tospecify loci for insertion of cryoprobes 266 and to specify a mode ofoperation of cryoprobes 266, and then utilize predictor 290 andevaluator 300 to predict whether, under his specified intervention plan,his/her goal will be realized and all tissues desired to be cryoablatedwill in fact be destroyed. Similarly, an operator may utilize predictor290 and evaluator 300 to predict whether, under his/her specifiedintervention plan, tissues which he specified as requiring protectionfrom damage during cryoablation will in fact be endangered by hisplanned intervention.

Recommender 310 may use predictive capabilities of predictor 290 andevaluator 300, or empirically based summaries of experimental andclinical data, or both, to produce recommendations for cryoablationtreatment.

As discussed above, predictor 290 and evaluator 300 can be used todetermine, for a given placement of a given number of cryoprobes and fora given set of operating parameters, whether a planned cryoablationprocedure can be expected to be successful, success being defined asdestruction of tissues specified as needing to be destroyed, with nodamage or minimal damage to tissues specified as needing to be protectedduring cryoablation. Based on this capability, recommender 310 canutilize a variety of calculation techniques well known in the art toevaluate a plurality of competing cryoablation intervention strategiesand to express a preference for that strategy which is most successfulaccording to these criteria.

In particular, recommender 310 may consider several interventionstrategies proposed by an operator, and recommend the most successfulamong them. Alternatively, an operator might specify a partial set ofoperating parameters, and recommender 310 might then vary (progressivelyor randomly) additional operating parameters to find a ‘best fit’solution. For example, an operator might specify tissues to bedestroyed, tissues to be protected, and a two-dimensional array ofcryoprobes such as, for example, the two dimensional placement array ofcryoprobes determined by the use of guiding element 115 having a net ofapertures 120 shown in FIG. 8 hereinabove. Recommender 310 could thentest a multitude of options for displacements of a set of cryoprobes ina third (depth) dimension to determine the shallowest and deepestpenetration desirable for each cryoprobe. Recommender 310 could furtherbe used to calculate a temperature and duration of freezing appropriatefor each cryoprobe individually, or for all deployed cryoprobescontrolled in unison, in a manner designed to destroy all tissuesspecified to be destroyed, while maximizing protection of tissuesspecified to be protected.

Recommendation activity of recommender 310 may also be based onempirical data such as experimental results or clinical results. Table 2provides an example of a basis for making recommendations derived fromclinical observation.

TABLE 2 Recommended number of cryoprobes to treat BPH AmericanUrologists Number of Association cross-sections Questionnaire withstricture of Prostate Number Score the Urethra Volume of probes 0-7 1-325 2 0-7 1-3 40 2 0-7 2-5 40 2 0-7 1-3 50 2-3 0-7 2-5 50 2-3 0-7 1-3 602-3 0-7 2-5 60 3 0-7 2-5 100 4  8-19 1-3 40 2-3  8-19 2-5 40 2-3  8-191-3 50 2  8-19 2-5 50 2-3  8-19 1-3 60 3  8-19 2-5 60 3-4  8-19 2-5 1004 20-35 1-3 40 3 20-35 2-5 40 3 20-35 1-3 50 4 20-35 2-5 50 20-35 1-3 604 20-35 2-5 60 5 20-35 2-5 100 6

Table 2 relates to the treatment of BPH by cryoablation. Table 2 isessentially a table of expert opinion, wherein three criterions fordescribing the symptomatic state of a patient are related, by experts,to a recommendation for treatment. Table 2 was in fact compiled by agroup of experts in the practice of cryoablation utilizing a particulartool, specifically a tool similar to that described in FIG. 8hereinabove, yet a similar table may be constructed by other experts andfor other tools. Moreover, feedback from the collective clinicalexperience of a population of users of a particular tool may becollected over time, for example by a company marketing such a tool orby an independent research establishment, and such collected informationmay be fed back into recommender 310 to build a progressively betterinformed and increasingly useful and reliable recommendation system.

The first column of Table 2, the AUA score, is the score of aquestionaire in use by the American Urological Association which may befound in Tanagho E. A., and McAninich J. W., Smith's General Urology,published by McGraw-Hill, Chapter 23. The AUA score is an estimate ofseverity of symptoms as subjectively reported by a patient, and relatesto such urinary problems as incomplete emptying of the bladder,frequency of urination, intermittency, urgency, weak stream, straining,nocturia, and the patient's perceived quality of life as it relates tohis urinary problems.

The second and third columns of Table 2 relate to diagnostic criteriadiscemable from three-dimensional model 258 or from digitizedpreparatory images 254 from which model 258 derives. The second columnis a measure of the length of that portion of the urethra observed to beconstricted by pressure from a patient's prostate. The third column is ameasure of the volume of that patient's prostate. Table 2 constitutes abasis for recommending an aspect of a cryoablation treatment for BPH,specifically for recommending, in column four, an appropriate number ofcryoprobes to be used in treating a specific patient, based on threequantitative evaluations of his condition constituted by the columnsone, two and three of Table 2.

Reference is now made to FIGS. 12 a and 12 b, which is a flow chartshowing a method for automatically generating a recommendation relatingto a cryoablation procedure, utilizing the information of Table 2, orsimilar information, according to an embodiment of the presentinvention. In the specific example of FIGS. 12 a-12 b, the generatedrecommendation is relevant to cryoablation of tissues of a prostate fortreatment of BPH.

At step 320 of FIG. 12 a, first imaging modality 250 is used to createpreparatory images, which are digitized at step 322 to become digitizedpreparatory images 254. In the example presented, images 254 are crosssections of a prostate such as those generated by a series of ultrasoundscans taken at regularly intervals of progressive penetration into thebody of a patient, as might be produced by the ultrasound equipmentdescribed with reference to FIGS. 8-10 hereinabove.

At optional step 324, an operator marks or otherwise indicates, withreference to images 254, locations of tissues to be cryoablated or to beprotected, as explained hereinabove. At step 326 images 254 are input tothree-dimensional modeler 256, which creates three-dimensional model 258of the intervention site at step 328. Model 258, along with anyoperator-highlighted and classified regions of model 258, are displayedat step 329.

In a parallel process, raw materials for a recommendation are gathered.At step 330 clinical input in the form of an AUA score from aquestionnaire of a patient's symptoms is input. At step 332 a count ismade of the number of preparatory images 254 (cross-sections) of theurethra which show constriction to the urethra caused by pressure fromthe prostate tissue on the urethra. A count of cross-sections showingconstriction is here taken as an indication of the length of astricture. Determination of which cross-section images show signs ofconstriction may be made by an operator, or alternatively may be made byautomated analysis of images 256, using image interpretation techniqueswell known in the art. At step 334, information available tothree-dimension modeler 256 is used to automatically calculate thevolume of the prostate.

At step 336, information assembled at steps 330, 332, and 334 is used ina table-lookup operation to retrieve a recommendation for theappropriate number of probes to be used to treat the imaged specificcase of BPH.

At step 340, an operator optionally inputs specific boundary conditionswhich serve to limit recommendations by the system. Utilizing model 254created at step 328, operator-specified boundary conditions from step340, operator-specified identification of locations of specific tissuesto be ablated or protected from step 324, and a calculated recommendednumber of probes from step 336, a recommendation for optimal positioningof a recommended number of probes may be made at step 342. Display of arecommended intervention is made at step 344.

Optionally, operator-specified placement of simulated cryoprobes maymodify or replace the recommended intervention, at step 346.

Step 344 is optionally iterative. That is, an operator may repeatedlymodify definitions of tissues, boundary conditions, or manual placementof simulated probes, until the operator is satisfied with the simulatedresults. As a part of step 344, activities of evaluator 300 may beevoked, so as to procure system feedback based on a simulatedintervention. Step 344 is repeated so long as desired by an operator,and until the operator is satisfied with the results.

Referring now to FIG. 12 b which is a continuation of the flowchart ofFIG. 12 a, at step 348 a final plan is optionally saved to a computerdisk or other memory 270.

In optional step 350, details of the completed intervention plan can beused to estimate and display expected long-term results of the plannedintervention, such as an expected future volume and shape of theprostate. Information from Table 2 or an equivalent is utilized for step350, as indicated at step 352. It is noted that long-term volume of theprostate may also be treated as a boundary condition of an intervention,at step 340.

The example presented in FIGS. 12 a and 12 b refers specifically to autilization of planning system 240 for treating a prostate for BPH.Similar utilizations may be contemplated, for treating other organs, orfor treating other conditions of a prostate.

In treating BPH, a desired goal is a reduction in prostate volume so asto relieve pressure on the urethra of a patient, because pressure on theurethra from an enlarged prostate interferes with the process ofurination. In treating BPH there is no need to destroy all of a selectedvolume, but rather simply to destroy some desired percentage of thatvolume.

In treating, for example, a prostate tumor suspected of malignancy,goals of the intervention are quite different. To avoid dangerousproliferation of malignant cells, it is desirable to ablate a definedvolume in its entirety. In such a context, when it is necessity todestroy all tissues within a selected volume, the functionality ofevaluator 300 of planning system 240 is particularly useful.

Evaluator 300 is able to calculate, for each arbitrarily selected smallvolume of model 258, the cumulative cooling effect of all cryoprobes inproximity to said selected small volume. Consequently evaluator 300 isable to make at least a theoretical determination of whether, for agiven deployment of cryoprobes utilized under a given set of operatingparameters, total destruction of malignant tissues within a selectedvolume is to be expected.

Reference is now made to FIG. 13, which is a chart showing temperatureprofiles for several cryoablation methods, useful for understandingFIGS. 14 and 15. FIG. 13 contrasts the temperature profiles forcryoablation used in prior art systems 354 as compared to thetemperature profiles 356 utilized according to the methods of FIGS. 14and 15.

Reference is now made to FIG. 14, which is a simplified flow chart of amethod for ensuring total destruction of a selected volume whilelimiting damage to tissues outside that selected volume, according to anembodiment of the present invention.

The method presented by FIG. 14 comprises (a) deploying a plurality ofcryoprobes in a dense array within a target volume, and (b) limitingcooling of the deployed cryoprobes to a temperature only slightly belowa temperature ensuring complete destruction of tissues. The temperatureprofile required is shown in detail in FIG. 13, where it is contrastedto a temperature profile according to methods of prior art. According tothe method of FIG. 14, limiting cooling of each cryoprobe has the effectof limiting the destructive range of each cooled cryoprobe. If aplurality of cryoprobes are deployed in an sufficiently dense array andcooled to an extent such as that indicated in FIG. 13, a nearly-uniformcold field is created, the field being uniformly below a temperaturerequired to ensure destruction of tissues within the field, yet there isrelatively little tendency for destructive temperature to extend farbeyond the deployed cryoprobe array. Thus, in contrast to methods of theprior art, the method presented by FIG. 14 relies on making a cryoprobearray more dense, and less cold. Control of degree of cooling may ofcourse be accomplished by controlling a temperature of cryoprobes of thearray, either individually or collectively, or by controlling durationof cooling of cryoprobes of the array, or both.

Reference is now made to FIG. 15, which is a simplified flow chart ofanother method for ensuring total destruction of a selected volume whilelimiting damage to tissues outside that selected volume, according to anembodiment of the present invention.

The method of FIG. 15 is similar to that of FIG. 14, in that it utilizesa dense array of cryoprobes cooled to a lesser extent than the coolingutilized according to methods of prior art. According to the method ofFIG. 15, however, cryoprobes at the periphery of a target volume arecooled less than are cryoprobes at the interior of the target volume.Cryoprobes at the interior of the target volume are, by definition,relatively distant from tissues desired to be protected, consequentlythey can be strongly cooled with impunity, thereby helping to ensuretotal destruction of target tissues. In contrast, cryoprobes near thesurface of the target volume are closer to healthy tissues, consequentlyit is desirable to cool them less, so as to limit the damage they cause.Such lesser cooling of surface cryoprobes is possible, withoutsacrificing efficient destruction of target tissues, because acombination of weak cooling from surface probes together with strongcooling from interior probes creates a near-uniform cold field near thesurface probes which ensures destruction of tissues on an interior sideof the surface probes, while causing relatively little destruction oftissues on an exterior side of the surface probes.

Planning system 240 can be used effectively to plan dense arrays ofcryoprobes according the methods of FIG. 14 and of FIG. 15. For example,a user might specify a particular density of an array of probes, thenuse evaluator 300 to evaluate a range of possible temperature andduration parameters to find an amount and duration of cooling whichensures that the specified array will indeed create a nearly-uniformcold field sufficient to destroy all target tissues. Alternatively, auser might specify a desired degree of cooling and use planning system240 to recommend a required density of the cryoprobe array.

Thus, evaluator 300 and recommender 310 can be used to calculatedplacement and operational parameters of cryoprobes in a manner whichguarantees a nearly-uniform cold field within a selected volume. Ifcryoprobes 266 are sufficiently small and placed sufficiently closetogether, cooling effects from a plurality of probes will influence eachselected small volume within a target volume, and an amount of requiredcooling can be calculated which will ensure that all of the targetvolume is cooled down to a temperature ensuring total destruction of thetarget volume.

In implementing the method of FIG. 15, control of degree of cooling mayof course be accomplished by controlling temperatures of cryoprobes ofthe array, either individually or collectively, or by controllingduration of cooling of cryoprobes of the array, or both.

Reference is now made to FIG. 16, which is a simplified block diagram ofa surgical facilitation system for facilitating a cryosurgery ablationprocedure, according to an embodiment of the present invention.

In a preferred embodiment, a surgical facilitation system 350 comprisesa first imaging modality 250 and optional digitizer 252, for creatingdigitized preparatory images 254 of an intervention site, a firstthree-dimensional modeler 256 for creating a first three-dimensionalmodel 258 of the intervention site based on digitized preparatory images254, a second imaging modality 360 with optional second digitizer 362for creating a digitized real-time image 370 of at least a portion ofthe intervention site during a cryosurgery procedure, and an imagesintegrator 380 for integrating information from three-dimensional model258 of the site and from real-time image 370 of the site in a commoncoordinate system 390, thereby producing an integrated image 400displayable by a display 260. Integrated image 400 may be a twodimensional image 401 created by abstracting information from a relevantplane of first three dimensional model 258 for combining with areal-time image 370 representing a view of that plane of that portion ofthe site in real-time. Alternatively, a set of real-time images 370 maybe used by a second three dimensional modeler 375 to create a secondthree dimensional model 402, enabling images integrator 380 to expressfirst three dimensional model 258 and second three dimensional model 402in common coordinate system 390, preferably a Cartesian coordinatesystem, thereby combining both images into integrated image 400.

Various strategies may be used to facilitate combining of model 258(based on preparatory images 254) with real-time images 370 (or model402 based thereupon) by images integrator 380. Processes of scaling ofimages to a same scale, and of projection of a ‘slice’ of a threedimensional image to a chosen plane, are all well known in the art.Basic techniques for feature analysis of images are also well known, andcan deal with problems of fine alignment of images from two sources,once common features or common directions have been identified in bothimages. Techniques useful for facilitating aligning of both images byimages integrator 380 include: (a) identification of common features inboth images by an operator, for example by identifying landmark featuressuch as points of entrance of a urethra into, and points of exit of aurethra from, a prostate, (b) identification of constant basicdirections, such as by assuring that a patient is in a similar position(e.g., on his back) during both preparatory imaging and real-timeimaging, (c) operator-guided matching, through use of interface 264, ofa first set of images, (d) use of proprioceptive tools for imaging, thatis, tools capable of reporting, either mechanically or electronicallyusing an electronic sensor 364 and digital reporting mechanism 365,their own positions and movements, and (e) using a same body of imagingequipment to effect both preparatory imaging, producing preparatoryimages 254, and real-time imaging during a cryosurgery procedure,producing real-time images 370. For example, using ultrasound probe 130of FIGS. 8-10 and FIG. 16 both for preparatory imaging and for real-timeimaging, and assuring that the patient is in a standard position duringboth imaging procedures, greatly facilitates the task of imagesintegrator 380. Equipping ultrasound probe 130 with stabilizer 366 andcontrolling its movements with stepper motor 367, as shown in FIG. 16,yet further simplifies the task of images integrator 380.

It will be appreciated that the present invention can benefit fromposition tracking of various components thereof so as to assist eitherin modeling and/or in actually controlling a cryoablation procedure.Position tracking systems per se are well known in the art and may useany one of a plurality of approaches for the determination of positionin a two- or three-dimensional space as is defined by asystem-of-coordinates in two, three and up to six degrees-of-freedom.Some position tracking systems employ movable physical connections andappropriate movement monitoring devices (e.g., potentiometers) to keeptrack of positional changes. Thus, such systems, once zeroed, keep trackof position changes to thereby determine actual positions at all times.One example for such a position tracking system is an articulated arm.Other position tracking systems can be attached directly to an object inorder to monitor its position in space. An example of such a positiontracking system is an assortment of three triaxially (e.g.,co-orthogonally) oriented accelerometers which may be used to monitorthe positional changes of the object with respect to a space. A pair ofsuch assortments can be used to determine the position of the object insix-degrees of freedom.

Other position tracking systems re-determine a position irrespective ofprevious positions, to keep track of positional changes. Such systemstypically employ an array of receivers/transmitters which are spread inknown positions in a three-dimensional space andtransmitter(s)/receiver(s), respectively, which are in physicalconnection with the object whose position being monitored. Time basedtriangulation and/or phase shift triangulation are used in such cases toperiodically determine the position of the monitored object. Examples ofsuch a position tracking systems employed in a variety of contexts usingacoustic (e.g., ultrasound) electromagnetic radiation (e.g., infrared,radio frequency) or magnetic field and optical decoding are disclosedin, for example, U.S. Pat. Nos. 5,412,619; 6,083,170; 6,063,022;5,954,665; 5,840,025; 5,718,241; 5,713,946; 5,694,945; 5,568,809;5,546,951; 5,480,422 and 5,391,199, which are incorporated by referenceas if fully set forth herein.

Position tracking of any of the imaging modalities described hereinand/or other system components, such as the cryoprobes themselves,and/or the patient, can be employed to facilitate implementation of thepresent invention.

In a preferred embodiment, surgical facilitation system 350 furthercomprises all functional units of planning system 240 as describedhereinabove. That is, facilitation system 350 optionally comprisessimulator 260 having user interface 264 with highlighter 280, eachhaving parts, functions and capabilities as ascribed to them hereinabovewith reference to FIG. 11 and elsewhere. In particular, system 350includes the above-described interface useable by an operator to specifyplacements and operational parameters of simulated cryoprobes 266, andto specify tissues to be cryoablated or to be protected duringcryoablation.

Similarly, facilitation system 350 further optionally comprises memory270, predictor 290, evaluator 300, and recommender 310, each havingparts, functions and capabilities as ascribed to them hereinabove withreference to FIG. 11 and elsewhere.

Thus, in a preferred embodiment of the present invention, facilitationsystem 350 is able to undertake all activities described hereinabovewith respect to planning system 240. In addition, facilitation system350 is able to provide a variety of additional services in displayingand evaluating at least one real-time image 370, and is further able tocompare real-time images 370 to three dimensional model 258, and also tocompare information from real-time images 370 to stored information suchas that identifying operator-specified tissues to be cryoablated or tobe protected, as is explained more fully hereinbelow.

In a preferred embodiment, either first imaging modality 250 and/orsecond imaging modality 360 may each independently be a magneticresonance imaging system (MRI), an ultrasound imaging system, acomputerized tomography imaging system (CT), some combination of thesesystems, or some similar system able to produce images of the internaltissues and structures of the body of a patient, yet in the case ofsecond imaging modality 360, ultrasound and MRI imaging are moretypically used, as being more conveniently combined with cryosurgeryprocesses.

Facilitation system 350 further comprises a first comparator 390, forcomparing first three-dimensional model 248 with real-time image 370,particularly to discern differences between both images. Suchdifferences constitute differences between a status of a plannedintervention and a status of an actual intervention in real-time. Tools,such as cryoprobes, tissues, such as a urethra, and ice-balls formedduring cryoablation, all figure as elements in three dimensional model258, and all may be visualized using second imaging modality 360. Thus,their expected positions, sizes, orientations, and behaviors may becompared to their actual real-time positions, sizes, orientations andbehaviors during cryoablation, by comparator 390.

Differences thereby revealed, and information concerning suchdifferences, can be of vital importance to an operator in guiding hisactions during an intervention, particularly if the operator deviatesfrom a planned intervention without being aware of doing so. Arepresentation of the revealed differences may be displayed by displayer262 and highlighted for greater visibility. A feedback mechanism 392,for example an auditory feedback mechanism, may be used to drawattention of an operator to serious discrepancies between a planned andan actual intervention.

Similarly, comparator 390 can be used to compare status of objectsvisible in real-time images 370 with stored information aboutoperator-specified tissues to be cryoablated. Comparator 390 can thusprovide information about, and displayer 262 can display, situations inwhich tissues intended to be cryoablated are in fact not effectivelybeing cryoablated by a procedure. Similarly, comparator 390 can be usedto check status of objects visible in real-time images 370, relatingthem to stored information about operator-specified tissues which are tobe protected during cryoablation. In the case of discrepancies betweenan actual situation and an operator-specified desirable situation,display 262 and feedback mechanism 392 can warn an operator when aprocedure seems to be endangering such tissues.

The capabilities of facilitation system 350 may extend yet further, todirect guidance to an operator in the manipulation of cryoablationtools, and even to partial or complete control of such tools during aphase of a cryoablation intervention.

Reference is now made to FIG. 17, which is a schematic diagram ofmechanisms for control of cryosurgical tools by a surgical facilitationsystem, according to an embodiment of the present invention.

A cryosurgical probe 50 is shown passing through an aperture 120 in aguiding element 115 which is realized in this example as a plate 110. Asdescribed hereinabove in the context of the discussion of FIGS. 8-10,aperture 120 is for limiting sideways movement of probe 50, which ishowever free to move forward and backwards towards and away from acryoablation site in a patient. In the prior art methods presented inFIGS. 8-10, such movement was conceived as under sole and exclusivecontrol of an operator who advanced and retracted probe 50 manually.

As has been noted above, the simulation, evaluation, and recommendationcapacities of planning system 240 and facilitation system 350, based onpreparatory images 254 and three dimensional model 258, allow system 350to calculate a recommended maximum and minimum depth for at which eachcryoprobe 50 is to be used for cryoablation. Further, a cryoablationplan manually entered by an operator may also determine a maximum andminimum depth at which each cryoprobe 50 is to be used for cryoablation.

In a simple implementation of mechanical control based on informationfrom planning system 240 or facilitation system 350, planned maximum andminimum depths generated by those systems are communicated to anoperator who adjusts a mechanical blocking element 430 according to agraduated distance scale 432, in a manner which limits forward orbackward movement of probe 50 so as to prevent an operator fromunintentionally and unknowingly advancing or retracting probe 50 beyondlimits of movement planned for probe 50. Such an arrangement guides andaids an operator in use and control of probe 50 for effectingcryoablation according to a plan.

In a somewhat more sophisticated implementation, control signals 438from system 350 activate a stepper motor 434 to directly controlmovement of probe 50. Thus, under control of system 350 and according toa planned, simulated, examined and theoretically tested procedure,stepper motor 434 can advance probe 50 to a planned depth for performingcryoablation. System 350 can also send temperature control signals toheating gas valve 440 and cooling gas valve 442, thereby controlling aflow of heating gas from heating gas reservoir 444 and a flow of coolinggas from s cooling gas reservoir 446. Thus, under control of anintervention plan and utilizing mechanisms presented in FIG. 17, system350 is able to directly control some or all of a cryoablationintervention. Thus, in a typical portion of a cryoablation procedure,stepper 434 advances probe 50 a planned distance, cooling gas valve 442opens to allow passage of a gas which cools probe 50 to cryoablationtemperatures and maintains those temperatures for a planned length oftime, then cooling valve 442 closes to halt cooling. Optionally, heatinggas valve 440 then opens to allow passage of a gas which heats probe 50so as to melt tissues in contact with probe 50, thereby restoring to itfreedom of motion, whereupon stepper motor 434 can further advance orretract probe 50 to a new cryoablation position, at which new positionsystem 350 can optionally repeat this cryoablation process.

To ensure accuracy, movement of cryoprobe 50 may be monitored by amovement sensor 436. Moreover, all the facilities of system 350previously described, for comparing real-time positions of objects withplanned positions of those objects, can be brought to bear, to monitorthis independently controlled cryoablation process.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

1. A method for planning a cryosurgical ablation procedure, comprising:(a) utilizing a first imaging modality to create digitized preparatoryimages of an intervention site; (b) utilizing a three-dimensionalmodeler to create a three-dimensional model of said intervention sitebased on said digitized preparatory images; (c) utilizing a simulator tosimulate a cryosurgical intervention, which simulator comprises adisplayer operable to display in a common virtual space an integratedimage comprising a visualization of said three-dimensional model of saidintervention site and a virtual display of at least one simulatedcryoprobe inserted at least one selected locus; (d) utilizing apredictor to predict an effect on body tissues of a patient of operationof said at least one cryoprobe at said at least one selected locusaccording to selected operational parameters, said predictor beingoperable to predict size and shape of a prostate two or more weeks aftersaid operation of said at least one cryoprobe, thereby enabling to plansaid cryoablation procedure in view of said predicted effect; (e)utilizing a recommender to recommend a preference among a plurality ofoperating schema, wherein each schema presents one or moreuser-designated plans for placement and operation of said at least onecryoprobe.
 2. The method of claim 1, further comprising displaying, insaid integrated image, a visualization of an effect predicted by saidpredictor.
 3. The method of claim 1, wherein said simulator furthercomprises an interface useable by an operator for specifying at leastone operator-specified locus for insertion of said at least onesimulated cryoprobe.
 4. The method of claim 1, wherein said simulatorfurther comprises an interface useable by an operator for specifyingoperator-specified parameters for operation of said at least onesimulated cryoprobe.
 5. The method of claim 1, wherein said simulatorfurther comprises a second recommender operable to recommend a positionfor inserting a cryoprobe into a body of a patient.
 6. The method ofclaim 1, wherein said simulator further comprises a second recommenderfor recommending operating parameters for a cryoprobe inserted in a bodyof a patient.
 7. The method of claim 1, further comprising using saidpredictor to predictor size and position of an iceball created byoperation of said at least one simulated cryoprobe.
 8. The method ofclaim 1, further comprising using said predictor to predict size andposition of an iceball created by operation of said at least onesimulated cryoprobe.
 9. The method of claim 1, further comprising usinga second recommender to recommend temperature and duration for coolingof said at least one simulated cryoprobe.